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The attacks were aimed at Shiite pilgrims trekking and driving to a shrine in Baghdad

The shrine to al-Kadhim in Baghdad is one of Shiite Islam's holiest sites

Casualties from Wednesday's wave of attacks across Iraq rose to 93 people dead and 312 wounded, the Interior Ministry said Thursday, making it the deadliest day in the country since the United States withdrew its troops in December.

The attacks were mostly aimed at Shiite pilgrims trekking and driving to a shrine in Baghdad.

The scale of violence left some stunned.

"I am deeply shocked and utterly dismayed by the despicable attacks across Iraq today that have claimed the lives of scores of Iraqis, including many pilgrims, and have injured dozens more," Martin Kobler, the U.N. secretary-general's special representative for Iraq, said Wednesday.

"The scale of the violence is disturbing. I urgently appeal to the government to address the root causes of the violence and terrorism that are causing so much suffering and pain to the Iraqi people."

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The U.S. Embassy in Baghdad said the attacks "killed and wounded innocent men, women, and children of all religious and ethnic backgrounds."

"The perpetrators of these cowardly terrorist attacks must be brought to justice and we will support Iraq's Security Forces in this effort in any way we can."

Iraqi Prime Minister Nuri al-Maliki met with Tony Blinken, U.S. Vice President Joe Biden's national security adviser, in Baghdad on Thursday. The two men discussed U.S.-Iraqi relations, but it is unclear whether they talked about the attacks.

En route from across the country, including the Shiite heartland of southern Iraq, pilgrims have been headed to the Imam Kadhim shrine in the Kadhimiya neighborhood of Baghdad. The event culminates Saturday when the faithful commemorate the death of Imam Moussa al-Kadhim, one of 12 revered imams in Shiite Islam.

The violence sparks fears of a renewal of the fighting between Sunnis and Shiites in Iraq in the last decade, a longtime animosity intensified by the U.S. invasion of Iraq and the toppling of the Saddam Hussein regime.

Most people in Iraq are Shiites, but under Hussein, Sunnis held a great deal of power despite their minority status.

Shiites gained the upper hand politically after Hussein was overthrown by a U.S.-led invasion in 2003. Sunnis felt disenfranchised amid that political backdrop, and many backed insurgent actions against the government.

As a result, Sunni-Shiite violence exploded in the 2000s. The violence eventually ebbed as the war wound down, but ever since, there have been spurts of high-profile attacks.

One of the deadliest days recently came on January 5 when at least 60 people were killed in attacks that again targeted Shiites on a pilgrimage.

But Wednesday's violence eclipses that day and is reminiscent of last decade's sectarian strife.

More than 100 people died in three separate actions as recently as 2009.

A string of suicide bombs in December of 2009 left 127 people dead. And two car bombs outside Baghdad's province building and the Justice Ministry in October of that year killed 160 people. In August, two truck bombings and three other blasts left at least 100 people dead.

Al Qaeda's umbrella group in Iraq, a Sunni group that has targeted Shiites, claimed responsibility for those attacks.